Preparation and characterization of hexadecyl trimethyl ammonium bromide (HDTMA-Br)-modified cellulose nanocrystals (CNCs) derived from South African waste agricultural residue (Corncobs)

Abstract

To address the challenges associated with waste management in South Africa, agro-waste products such as corncobs can be valorized into value-added materials like cellulose nanocrystals (CNCs), thus paving the way for the circular economy. This study investigated the extraction of CNCs from South African waste corncobs through mixed acid hydrolysis using a mixture of sulfuric acid and oxalic acid dihydrate in a mass ratio of 1:5. For the first time, CNCs obtained from South African waste corncobs were functionalized using hexadecyl trimethyl ammonium bromide (HDTMA-Br) to enhance their usability in a variety of applications. Characterization techniques such as: Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infra-red (FTIR) spectroscopy, X-ray Diffraction (XRD), and Thermogravimetric analysis (TGA), were used to examine the surface morphology, surface functional groups, crystallinity, and thermal degradation of the isolated and the functionalized CNCs, respectively. SEM images revealed that the waste corncobs were successfully pre-treated due to the fibrous structure and individual particles observed. The TEM image of the prepared CNCs showed needle-shaped nanoparticles with an average diameter of 40 ± 1.11 nm, 178.5 ± 2.3 nm long, and 20.8 ± 1.7 nm wide. According to the XRD pattern, a strong peak showed at2Θ = 22.4(degree) was considered for the determination of the crystallinity of raw cellulose and that of the CNCs. About 64.5% and 78.9% crystallinity were obtained from the raw cellulose and the extracted CNCs, respectively, with approximately 55.25% yield. FTIR spectra of the functionalized CNCs showed the attachment of new functional groups, methyl, and methylene groups, onto the fCNCs’ surface. Furthermore, TGA analysis indicated that functionalized CNCs were more thermally stable compared to non-functionalized CNCs. These findings showed successful isolation and modification of CNCs from South African waste corncobs for their prospective use in wide-ranging applications.